Spark plugs?
R75/5 Misfire.
- Thread starter talaris
- Start date
Brand new.
I had a similar issue many years ago and seem to remember that one of coils had rotated in its clamp and the spade terminal was arcing/shorting out on the tank or frame but can't remember if it was all the time or only when revving the engine
Float needle sticky? Either flooding or starving the misfiring side?
Idle circuit blocked?
Valve not seating?
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Idle circuit blocked?
Valve not seating?
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Beemerboff
Registered user
On my R75/7 the arrangement which holds the carb needle was past its best.
There is a thin wire C clip which holds the needle and it is held in place by what looks like a star washer, and neither was doing what they were meant to do and the needle was moving around.
Which gave symptoms similar to yours, but not so pronounced.
'bins and 'works had both parts between them back then, dont know about now.
There is a thin wire C clip which holds the needle and it is held in place by what looks like a star washer, and neither was doing what they were meant to do and the needle was moving around.
Which gave symptoms similar to yours, but not so pronounced.
'bins and 'works had both parts between them back then, dont know about now.
Really appreciate all the help.
Governor looks ok but frankly I probably wouldn’t recognise if it didn’t.
Ran it tonight. Idles fine but garage smells of gases quite heavily so it’s obviosly rich.
It’s only on one side as it runs fine on one side if the plug cap is off and won’t run on the other if the cap is off.
Interestingly my temp sensor shows it much hotter on the “good” side than the other.
I hadn't seen this post. This then narrows it down to one side and a fuel problem. You could try swapping the bits like float control needle and seat, metering needle and clips etc. from the good side to the bad side and see what happens. If it's running rich on the cool side that doesn't surprise me as the excess fuel is serving to cool it.
A ploy i have used a number of times to diagnose a fault is to turn off the petrol and see what effect that has as the fuel level drops. Also if you know the problem is on one side just pinch the fuel feed pipe to that side and starve it of fuel to see the result.
Or not being ignited because of an electrical problem!
From what the OP has told us it appears to be an excess of fuel that is causing the problem.
"Ran it tonight. Idles fine but garage smells of gases quite heavily so it’s obviously rich"
The fact that there is a misfire will serve to keep the temperature down i will agree but a surfiet of fuel is very likely to be the real reason for the lower temperature though. Imho of course.
What do the plugs look like if you take them out immediately after running the bike?
Deleted account 220427001
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check carb inlet rubbers if there are cracked or split and the breather on the fuel tank
If you have not done this, check the small filters immediately UNDER each fuel tap - unscrew nut connector and the filter will be visible.
Just a thought.
I run a 1973 R75/5 and refurbished it after it had been off the road for 28 years - took a while to sort out several little issues but now runs a treat - fitted Boyer Bransden electronic ignition too.
Mike
Just a thought.
I run a 1973 R75/5 and refurbished it after it had been off the road for 28 years - took a while to sort out several little issues but now runs a treat - fitted Boyer Bransden electronic ignition too.
Mike
Resolved
Well it was Rob Farmer who put me on the right lines.
Checked the governor with the cover off and sparks flying everywhere! The points were arcing out and little adjustment stopped that.
Then started from scratch with the carbs.Re adjusted the throttle cables, stated with each mixture screw even, got the ticker correct and equal on each pot and the sorted out the mixture. Re-adjusted the ticker and job done. Replaced diaphragms, inlet rubbers, throttle springs, leads plugs, coils, condenser, governor springs, choke bodies and to be fair they all need doing as they were old.
Something so bloody simple............still all the ignition parts are now new so the re-bore it has just had its good for another 47 years.
Thanks everybody
Well it was Rob Farmer who put me on the right lines.
Checked the governor with the cover off and sparks flying everywhere! The points were arcing out and little adjustment stopped that.
Then started from scratch with the carbs.Re adjusted the throttle cables, stated with each mixture screw even, got the ticker correct and equal on each pot and the sorted out the mixture. Re-adjusted the ticker and job done. Replaced diaphragms, inlet rubbers, throttle springs, leads plugs, coils, condenser, governor springs, choke bodies and to be fair they all need doing as they were old.
Something so bloody simple............still all the ignition parts are now new so the re-bore it has just had its good for another 47 years.
Thanks everybody
Good result 
Great Stuff! Glad you got to the bottom of things.
